This invention relates generally to electronically controlled fuel injection systems and, more particularly, to a method and apparatus for determining a desired duration at which to set a delay during multiple shot fuel injections for each injector device of the injection system.
Electronically controlled fuel injectors are well known in the art including hydraulically actuated and mechanically actuated electronically controlled fuel injectors. An electronically controlled fuel injector typically injects fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are increasingly becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, particulate and nitrogen oxides (NOx). Tailoring the number and the parameters of the injection fuel shots during a particular injection event are ways in which to control emissions and meet such emission standards. As a result, techniques for generating split or multiple fuel injections during an injection event have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emissions and noise levels. Generating multiple injections during an injection event typically involves splitting the total fuel delivery to the cylinder during a particular injection event into two or more separate fuel injections, generally referred to as a pilot injection fuel shot, a main injection fuel shot and/or an anchor injection fuel shot. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine operation and emissions control.
In the past, the controllability of split or multiple injections has been somewhat restricted by mechanical and other limitations associated with the particular types of fuel injectors utilized. For example, when delivering a split or multiple injection current waveform to a plurality of fuel injectors, some injectors will actually deliver the split fuel delivery to the particular cylinder whereas some injectors will deliver a boot fuel delivery. A boot type of fuel delivery generates a different quantity of fuel as compared to a split type fuel delivery since in a boot type delivery, the fuel injection flow rate never goes to zero between the respective fuel shots. Conversely, in a split fuel delivery, the fuel injection flow rate does go to zero between the respective fuel shots. As a result, more fuel is delivered in a boot type delivery as compared to a split fuel delivery. Even with more advanced electronically controlled injectors, during certain engine operating conditions it is still sometimes difficult to accurately control fuel delivery.
When dealing with split or multiple fuel injection and the general effects of a boot type fuel delivery and the fuel injection rate shaping which results therefrom, desired engine performance is not always achieved at all engine speeds and engine load conditions. Based upon operating conditions, the injection timing, fuel flow rate and injected fuel volume are desirably optimized in order to achieve minimum emissions and optimum fuel consumption. This is not always achieved in a multiple injection system due to a variety of reasons including limitations on the different types of achievable injection rate waveforms and the timing of the fuel injections occurring during the injection events. As a result, problems such as injecting fuel at a rate or time other than desired within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect emission outputs and fuel economy. From an emissions standpoint, either a split or boot fuel delivery may be preferable, depending on the engine operating conditions.
In a system in which multiple injections and different injection waveforms are achievable, it is desirable to control and deliver any number of separate fuel injections to a particular cylinder so as to minimize emissions and fuel consumption based upon the operating conditions of the engine at that particular point in time. This may include splitting the fuel injection into more than two separate fuel shots during a particular injection event and/or adjusting the timing between the various multiple fuel injection shots in order to achieve the desired injector performance, that is, a split or a boot type fuel delivery, based upon the current operating conditions of the engine.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, there is disclosed an electronically controlled fuel injection system which is capable of delivering multiple fuel injections to a particular cylinder of an internal combustion engine during a single injection event. The present system includes means for variably determining whether two, three, or more separate fuel injections or fuel shots are desired during a fuel injection event at given engine operating conditions including engine speed and engine load. In this regard, in a preferred embodiment, fuel is apportioned between a first or pilot shot, a second or main shot and a third or anchor shot, each separate fuel injection shot being delivered when the cylinder piston is located within a predetermined range during a particular piston stroke. The present system also includes means for varying the timing and fuel quantity associated with the main shot, the timing and the fuel quantity associated with the anchor shot, as well as the duration of the anchor delay, based upon the operating conditions of the engine.
Under certain operating conditions, the proximity of the main and anchor shots and the resultant internal injector hydraulics and/or mechanics leads to a rate shaping effect of the third or anchor injection. As a result, although the first or pilot injection, when used, is typically a distinct injection as compared to the second, or main, and the third, or anchor, injections, a distinct anchor injection is not always apparent. The present invention enables determination as to whether a given injector is delivering a distinct third shot and, based upon considerations such as engine performance, minimization of emissions, injector durability and so forth, the present system alters the anchor shot delay, if necessary, to achieve the desired injector performance.